A combined X-ray diffraction and Raman scattering study of the phase transitions in Sr_1−xCa_xTiO₃ (x=0.04, 0.06, and 0.12)

Abstract

Results of powder X-ray diffraction and Raman scattering studies on the phase transitions in Sr_1−xCa_xTiO₃ (SCT) are presented for , 0.06 and 0.12 in the temperature range 8–473 K. It is proposed that the space group of SCT in the composition range is with tilt system and not with tilt system, as assumed by earlier workers. The lowering of the crystal symmetry from to is supported by the observation of additional Raman lines, in agreement with the factor group analysis for the space group. The structural Eg mode, characteristics of the non-cubic phase, is shown to be present even in the cubic phases of and but not of indicating the change in the local structure of the cubic phase of SCT for . The presence of symmetry forbidden TO₂ mode in the Raman spectra of the cubic phase of SCT for and its absence for provides yet another characteristic feature distinguishing the and space groups. The implications of the change in the tilt system from to on the development of the polar order is also discussed.